The present invention relates to a method for producing tubular plastic containers and, more specifically, to producing tubular plastic containers from a tubular sleeve, having an open neck at one end and an open end at the other end, by closing the open end thereof with an integral sealed bottom wall.
Thermoplastic tubular containers, especially collapsible or squeezable containers, have continued to take over an increasing share of the container market from metallic tubes. Such thermoplastic tubular containers are extensively used in packaging of cosmetics, medicinal preparations, shampoos and other products. With the increased development of multilayer or laminated tubes having oxygen barrier properties, that resist oxygen, or other gas permeation, further increases in packaging of pharmaceutical products and of foodstuffs in thermoplastic tubes are occurring. In addition to the packaging of products for use by consumers in a collapsible tube form, the use of collapsible thermoplastic containers or bag-like receptacles are also used in aerosol can applications where the product to be sprayed from the aerosol can is protected in a thermoplastic container separate from a pressurized fluid which is, in turn, contained within an outer shell, such as a metallic pressure resistant can.
One process for the formation of thermoplastic tubular containers is described in Myron H. Downs, U.S. Pat. No. 3,047,910 the contents of said patent incorporated by reference herein. As described therein, thermoplastic tubular containers are fabricated by placing a thermoplastic tubular member, or hollow tube, into a forming collar and forcing a cut, molten disc into an open end of the tubular member. The latent heat of the molten disc is sufficient to weld the peripheral edge of the disc to the inner wall of the tubular member and thus, form an end closure or head for the tubular container. As described, pressure is exerted through the interior of the tubular container to the sealed end closure to shape the latter to a desired contour The preferred means for applying pressure to the sealed end closure is through the use of a mandrel that is inserted through the open end of the tubular member. Air pressure or vacuum are not suggested for forming the contour of the sealed end closure, although it is suggested that air under suitable pressure or a reciprocable flat end mandrel may be admitted interiorly of the tubing to assure that a flat end-closure is not distorted upon cooling and remains desirably flat.
A further process for forming collapsible thermoplastic tubular containers is described in U.S. Pat. No. 3,962,006. In that process, a laminated film is used to form a thermoplastic sleeve having an impermeable layer, and a molten disc also having an impermeable layer is welded to the interior wall of the laminated thermoplastic sleeve. A pressing operation is used to form a head member on the tube, the pressing operation using a female mold and a core which interiorly supports the laminated thermoplastic sleeve.
These processes relate to the formation of headed sections on tubular sleeves and are usable only when a fully open end of the container is provided opposite the headed section to be formed, for insertion of a headed core or internal mandrel into the interior of the tubular sleeve to press the headed section into conformity with a female mold. When the other end wall or bottom of the tubular container is formed, such is normally formed merely by heat sealing transversely across the bottom to close the same. In the formation of such a transverse heat sealed bottom, however, flared or webbed portions result at the opposite ends of the transverse seal which can be detrimental in certain applications, and also results in a container that cannot be supported freely by the bottom wall on a flat surface.
In formation of collapsible thermoplastic tubes in the nature of a bottle or bag for use in aerosol containers, the flared portion on the transversely sealed bottom wall is not desirable due to the space limits of the aerosol can in which the tube is to be used.
It is an object of the present invention to provide a process for sealing integrally a bottom wall to a thermoplastic tubular container having an open neck at the top end thereof.